1. Field of the Invention
The present invention relates to a display device, and more particularly, to a transflective liquid crystal display device and a manufacturing method thereof that selectively operate in a reflective mode or a transmissive mode.
2. Discussion of the Related Art
Liquid crystal display (“LCD”) devices can be classified into a transmissive type using a backlight as a light source and a reflective type using natural or artificial light without using the backlight. A transmissive LCD device displays a bright image even in dark environments by using a backlight as a light source. However, the transmissive LCD device consumes a large amount of power. On the other hand, the reflective LCD device does not use a backlight and thus consumes a low amount of power. However, the reflective LCD device cannot be used when an external environment is dark.
A transflective LCD device has been developed to address these problems. A transflective LCD device includes both a reflective region and a transmissive region in a unit pixel region, and thus has both functions of the transmissive LCD device and the reflective LCD device. Also, because the transflective LCD device uses both light from a backlight and natural or artificial light from the outside, it is not restricted by peripheral environments and consumes a small amount of power.
FIG. 1 is an exploded perspective view of a transflective type LCD device according to the related art, and FIG. 2 is a cross-sectional view of the transflective type LCD device shown in FIG. 1. In FIG. 1, a transflective LCD device 11 includes an upper substrate 15, a lower substrate 21 and a liquid crystal layer 14 therebetween. The upper substrate 15 includes a common electrode 13 formed on a black matrix 16 and a sub-color filter 17.
The lower substrate 21, which is often referred to as an array substrate, includes a plurality of gate lines 25 and data lines 39. A pixel region P is defined by the intersections between the gate and data lines 25 and 39 and includes a transmissive region B and a reflective region D. A switching element T is formed at each pixel region P. The pixel region P also includes a reflective electrode 49 and a transparent pixel electrode 61.
As shown in FIG. 2, the reflective electrode 49 having a transmission hole A is formed on the lower substrate 21 over the transparent pixel electrode 61. A backlight 91 is disposed under the lower substrate 21.
When the transflective LCD device 11 operates in a reflective mode, it uses natural or artificial light from the outside as a light source. Light F2 incident on the upper substrate 15 is reflected by the reflective electrode 49. The reflected light penetrates the liquid crystal layer 14 arranged by an electric field generated between the reflective electrode 49 and the common electrode 13. In particular, the amount of light penetrating the liquid crystal layer 14 is adjusted by the arrangement of liquid crystal molecules in the liquid crystal layer 14, thereby displaying an image.
In a transmissive mode, the transflective LCD device 11 uses light F1 from the backlight 91 as a light source. Light emitted from the backlight 91 passes through the transparent pixel electrode 61 and penetrates the liquid crystal 14 arranged by an electric field generated between the common electrode 13 and the transparent pixel electrode 61. In particular, the amount of light penetrating the liquid crystal layer 14 is adjusted by the arrangement of liquid crystal molecules in the liquid crystal layer 14, thereby displaying an image.
FIG. 3 is a detailed plan view of a portion of an array substrate of a transflective LCD device according to the related art. In FIG. 3, a gate pad electrode 27 is formed at one end of the gate line 25. The gate pad electrode 27 is formed wider than the gate line 25. A data pad electrode 41 is formed at one end of the data line 39. The data pad electrode 41 is formed wider than the data line 39. The gate pad electrode 27 and the data pad electrode 41 contact a transparent gate pad terminal electrode 63 and a transparent data pad terminal electrode 65, respectively, which directly receive external signals.
A pixel region P is defined by the gate and data lines 25 and 39 intersecting each other. The pixel region P includes a transparent pixel electrode 61 and a reflective electrode 49 with a transmission hole A, and thus is divided into a transmissive region B and a reflective region D.
The pixel region P also includes a thin film transistor T having a gate electrode 23, a source electrode 35, a drain electrode 37, and an active layer 31 on the gate electrode 23. A storage capacitor C is disposed on a portion of the gate line 25, and is connected in parallel to a transparent pixel electrode in the pixel region P.
The storage capacitor C includes a first capacitor electrode formed by a portion of the gate line 25 and a second capacitor electrode formed by a source-drain metal layer 43 disposed on the portion of the gate line 25. The source-drain metal layer 43 is formed on the same layer and of the same material as the drain electrode 37. The second capacitor electrode 43 may be connected through a contact hole 55 to the pixel electrode 61. Alternatively, the second capacitor electrode 43 may be extended to the drain electrode 37 through a lower portion of the reflective electrode 49 and over the gate line 25, such that the contact hole 55 is omitted.
FIG. 4 is a cross-sectional view taken along II-II′, III-III′ and IV-IV′ of FIG. 3. As shown in FIG. 4, a gate electrode 23 and a gate line 25 are formed on a substrate 21, and a gate pad electrode 27 is formed at one end of the gate line 25. A gate insulating layer 29 is formed on an entire surface of the substrate 21 covering the gate electrode 23, the gate line 25 and the gate pad 27.
An active layer 31 and an ohmic contact layer 33 are formed on the gate insulating layer 29 above the gate electrode 23. Next, source and drain electrodes 35 and 37 contacting the ohmic contact layer 33, a data line 39 connected to the source electrode 35, and a data pad 41 disposed at one end of the data line 39 are formed on the gate insulating layer 29. Also, a source-drain metal layer 43 is formed on a portion of the gate line 25 in the pixel region P.
An insulating material is deposited on the resulting structure of the substrate 21 to form a passivation layer 45. The passivation layer 45 is an inorganic insulating layer formed by depositing silicon nitride (SiN.sub.x) or silicon oxide (SiO.sub.2).
A transparent organic insulating material is deposited on the passivation layer 45 to form an organic insulating layer 47. The transparent organic insulating material is one of benzocyclobutene (BCB) and acryl-based resin. An uneven pattern 47b is formed on the reflective region D on the organic insulating layer 47.
The gate insulating layer 29, the passivation layer 45 and the organic insulating layer 47 are etched to form a through-hole 48. The through-hole 48 corresponds to a transmission hole of a reflective electrode that will be formed in a subsequent process.
The passivation layer 45 and the organic insulating layer 47 are etched to form a drain contact hole 53 exposing a portion of the drain electrode 37, a storage contact hole 55 exposing a portion of the source-drain metal layer 43, a gate pad contact hole 57 exposing a portion of the gate pad electrode 27, and a data pad contact hole 59 exposing a portion of the data pad electrode 41.
A transparent conductive metal is deposited on the entire surface of the resulting structure of the substrate 21 and the deposited metal is patterned to form a transparent pixel electrode 61 in the pixel region P contacting the drain electrode 37 and the source-drain metal layer 43, a gate pad terminal electrode 63 contacting the gate pad electrode 27, and a data pad terminal electrode 65 contacting the data pad electrode 41. The transparent conductive metal is one of indium-tin-oxide (ITO) and indium-zinc-oxide (IZO). In particular, the pixel electrode 61 is formed in the reflective region D in an uneven structure in accordance with the uneven pattern 47b of the organic insulating layer 47.
A metal, such as aluminum (Al) or Al alloy, is deposited on the entire surface of the substrate 21 where the through-hole 48 has been formed. The deposited metal is patterned to form a reflective electrode 49 having a transmission hole A corresponding to the through-hole 48. The reflective electrode 49 is in an uneven structure in accordance with the uneven structure of the pixel electrode 61 and the organic insulating layer 47.
However, the above related art method requires the depositing and patterning processes for forming the above uneven pattern and structure on an array substrate, thereby reducing manufacturing yield. For example, an array substrate can be rejected and wasted due to a defect in one of the patterning process, e.g, a defect in manufacturing the switching element thereon or a defect in manufacturing the reflective electrode thereon. Especially, since the complexity and cost for manufacturing the switching elements is higher, a defect in a later process of manufacturing the reflective electrode can spoil previous efforts in manufacturing the switching elements.
Also, an adhesion problem may occur between the organic insulating layer and one of the passivation layer and the pixel electrode due to the uneven structure, thereby reducing product quality.